It has been observed that the pad of a gecko's foot is comprised of hundreds of thousands of setae. Setae are small hairs that split into hundreds of much smaller hairs called spatula. It was hypothesized and eventually proven that the adhesive force of the gecko was due these tiny hairs. The spatula of the gecko ranges about 200 nanometers to about 400 nanometers in diameter. It was determined that the adhesive force of the gecko was to due to intermolecular forces caused by the individual spatula. These forces, commonly known as Van der Waals forces, are weak attractive forces between atoms or non-polar molecules caused by a temporary change in dipole moment arising from a brief shift in orbital electrons to one side of one atom or molecule, creating a similar shift in adjacent atoms or molecules. Although Van der Waals forces are relatively weak, the spatula are so small and so many in number that the aggregate force is very strong.
Attempts at forming an adhesive microstructure based on the configuration of the gecko's foot includes forming a plurality of setae-like members having a plurality of spatulae-like protrusions by nanomolding using a template, polymer self-assembly, lithography, and etching.
There is a need for further methods for forming nanofiber adhesives structures where attachment is via Van der Waals forces.